As an update, buttoned up, reset gyros, turned AP on as a ground check - did exactly the same thing as above - left and right roll commanded ok, pitch commanded "up" regardless of what I told it to do, and "MAX AS" registered.

Went flying - when engaged AP, got an uncommanded right turning dive - had to disconnect. Reset gyros in flight, held course (not altitude) for 5 seconds, then descending right turn. "MAX AS" registered on the autopilot head and EFIS screen.

Phil